(a) Technical Field of the Invention
The present invention relates to a mechanism for suppressing noise caused by the operation of balance gear of an engine crankshaft, and in particular to a mechanism having less number of parts and being easy to assemble.
(b) Description of the Prior Art
FIG. 1 of the attached drawings shows an engine, which is broadly designated with reference numeral 1, and a transmission box 2 arranged at one side of the engine 1. A belt-based transmission mechanism 3 is encased in the transmission box 2. In operation, a mixture of fuel and air is fed into the engine 1 and an ignition device 11 ignites the mixture to cause combustion of the mixture inside a cylinder of the engine. The combustion results in expansion of gas inside the cylinder, which in turn drives a piston 12 to move reciprocally inside the cylinder. The piston 12 is coupled to a crankshaft 13, which extends into the transmission box 2 and is coupled to the transmission mechanism 3 to drive the transmission mechanism 3 for driving wheels of a vehicle on which the engine is mounted.
Also referring to FIG. 2, the piston 12 is coupled to the crankshaft 13 through a connecting rod 15 so that the movement of the piston 12 is converted into rotation of the crankshaft 13. A counterweight 16 is provided, in an eccentric manner, to the crankshaft 13 corresponding to the connecting rod 15. When the piston 12 is moved by the expansion of the combusted fuel-air mixture, the force acting on the piston 12 is transmitted to the counterweight 16 through the connecting rod 15, causing the crankshaft 13 to rotate about a rotational axis thereof. The counterweight 16, however, possesses a large inertial force, which induces vibration on the rotation of the crankshaft 13. To eliminate the vibration and maintain steady and stable rotation of the crankshaft 13, the engine 1 is provided with a balance shaft 4, which is coupled to the crankshaft 13 by having a drive gear 17 that is mounted on the crankshaft 13 mating a balance gear (driven gear) 41 mounted on the balance shaft 4. The drive gear 17 drives the driven gear 41 and thus causes the balance shaft 4 to rotate in unison with the crankshaft 13 for eliminating or compensating vibration caused by the inertial of the counterweight 16 of the crankshaft 13.
However, due to the manufacturing tolerance of the gears, backlash is present between teeth of the mated gears. Thus, noise is often generated when the drive gear 17 of the crankshaft 13 and the balance gear 41 of the balance shaft 4, which mate each other, are rotated in high speed during the operation of the engine 1.
FIG. 3 illustrates a solution for eliminating the gear noise caused by backlash, wherein the balance gear 4 is divided into two halves, one referred to as primary gear and designated with reference numeral 411, while the other secondary gear 412. The primary and secondary gears 411, 412 are arranged closely side by side. A torsional spring 42 is provided between the secondary gear 412 and a ring retainer 43 that is tightly fit over the balance shaft 4 and fixed in position by a pin 44 to maintain the secondary gear 412 close to the primary gear 411. The torsional spring 42 constantly induces an angular shift of the secondary gear 412 with respect to the primary gear 411 to eliminate the backlash between the drive gear 17 and the primary gear 411.
Further, the secondary gear 412 is allowed to take free rotation within a limited angular range so that when the drive gear 17 of the crankshaft 13 is to drive the balance gear 41 of the balance shaft 4, the drive gear 17 of the crankshaft 13 engages the secondary gear 412 first and the secondary gear 412, due to the elastic deformation of the torsional spring 42, is rotated a limited angular displacement about the balance shaft 4 until the teeth of the secondary gear 412 and the primary gear 411 completely align with each other. Thereafter, the drive gear 17 moves both the primary and secondary gears 411, 412 simultaneously to rotate the balance shaft 4.
This conventional mechanism, although effective in suppressing the noise caused by the gear backlash during the operation of the engine, has a complicated structure, which does not complicate the assembling process, but also increase costs, especially tightly fitting the ring retainer 43 to the balance shaft 4 causing significant trouble in manufacturing.
Thus, it is desired to provide a mechanism to solve the noise problem in a simple and efficient manner.